Today I completed my "do it yourself" Isotron with various results.
My first Isotron is built with a 3 meters PVC drain-pipe with a diameter of 63 mm.

I use a pair of "chicken-fence-net" (Excuse my English) capacitor hats with a size of 300x600 mm.
The coil is wound on the PVC tube with a little over 200 turns 1.5 mm electrical plastic insulated cable for 1600-1800 kHz. The antenna is fed via 50 ohm RG58 and before it gets to the antenna I wind it 30 turns on a ferrite core (1x10 inch) as an RF choke.

My first test was to drive this Isotron with 100 watts on 1640kHz. SWR was 1.5:1. I raised the Isotron about 2 meters above the ground. Bandwidth is like 10-15 kHz or even less.

I called a friend who has a long wire antenna. He lives about 85km from my place (shortest trip). Signal was S9 at 10.00 in the morning. The band was quiet except my S9 signal. I also drove away in my car with 100 watts peak modulation and I had to turn back home because it was heard too far away. I expect it can be heard easy 20-30 miles with good quality in a car radio with 100 watts.

The Isotron is an amazing antenna. Very hard to tune and SWR can vary very easily, but boy, this antenna really gets out.

Make sure you mount this antenna high, out of reach from humans. The voltage on the top cap is extremely dangerous, even at low power.

I'll post more info later as I am building a new Isotron with a larger coil diameter, this lowering the number of coil turns.

Regards

MosFet

Sun Mar 13, 2005 10:20 pm

erobertgCompulsive poster:)

Joined: 29 Oct 2004Posts: 113

Homebrew Isotron...

Actually the Isotron is an overgrown "L" network. Basically it is a coil and capacitor in a tuned circuit. The commercial version which is designed for 1650-1800 kHz (200B) can be tuned to extending the tuning rod to the top and adding a stub with approx 14 sq. in. above the coil to 1640kHz which I use.

The coil is wound on a 3.5" (4.00 O.D.) white PVC pipe with #14 solid house wire. This wire is cheap sells for about $15.00 for 500'. The coil is close wound 8.5" lg. @ approx 9 turns per inch.

The top rod is made from (2) 30" sections of 1/4" aluminum rods joined with a union. The top rod is connected to the capacitance hat with 1/4-20 SS nuts.

The roof or capacitance hat is approximately 1.3 sq ft (aluminum sheet) of area and so is the bottom hat.

The bottom capacitance hat is only connected to the ground on the coaxial connector and by a ground wire to the support mast.

There is nothing sacred about the geometry of capacitance hats but they should be a solid area. You could probably use (2) 16" dia or greater pizza pans.

It would probably look nicer with a symmetrical configuration using the pizza pans but would have to be supported with PVC pipe right up to the top.

Mon Mar 14, 2005 4:05 pm

MOSFETNew registered user

Joined: 26 Feb 2005Posts: 5

New ISOTRON

I have now completed a new Isotron for the lower part of the MW band on a 160mm PVC waste-pipe.
The pipe is 6 meters height and the distance between the two cap hats is 5 meters.
I wound 160 turns of 1.5 mm plastic insulated copper cable.
This unit resonates around 520 kHz.

I tried with 15 watts on 522 kHz and reached about 80km with S7 during daytime.
During nighttime it was also possible, but with heavy fading as it probably skipped in the atmosphere.

I have now completed a new Isotron for the lower part of the MW band on a 160mm PVC waste-pipe. SNIP

VERY INTERESTING!

Can you point me in the right direction about frequency vs. lenght reduction loss (from capacitive hat to capacitive hat) vs. efficiency?

My frequency is 1602 khz but I haven't much space to use (currently I made some hopeless experiments with a simple 2.3 mt vertical 12 mm. diameter with an LC base coupler.. But for my favorite AM I'm ready to try everything ).

I haven't find any serious documents about ISOTRON building on the web...

Many thanks

_________________** AM is a choice of life **
** FM is only a choice of fashion **

Thu Feb 02, 2006 10:42 am

OsiNew registered user

Joined: 04 Dec 2008Posts: 1

The Isotron 160c has worked well for me the past couple of years. Took awhile to put together, but once up it has allow me to work the Top Band from a home with a postage stamp sized lot. Four to five hundred miles is pretty common. I've also worked a few stations over 1K miles. You do have to have a good antenna turner and will need to re-turn even if you move only a few Khz. Doesn't work like a full wave dipole, but when you don't have 252 feet to work with, the Isotron will get you on the air. When I tell contacts that I'm using a Isotron, I often get "Those don't work," which is a bit silly when I'm talking to them on it.

I have search the net for some hours now to find some good instructions.

I wanna build an Isotron for 1602KHz. and need som good instructions. Size of the "end arrows" how many torns on the main coil, and feed for the koax and how to tune the antenna, basicly all info...

Thanks!

Ken

Sun Jan 04, 2009 6:23 pm

gitoNew registered user

Joined: 20 Mar 2009Posts: 1

Dear Mosfet

I lived in Indonesia,I build small M.W Transmitter for Gospel Radio,and I'm interested in your Isotronic antenna,because I can't build a full sizes quarter wave antenna,because we don't have enough land,especialy to place the ground radials.

Can you give me details,how to build such antenna (Isotron antenna).
It will be a great to me

I have now completed a new Isotron for the lower part of the MW band on a 160mm PVC waste-pipe.
The pipe is 6 meters height and the distance between the two cap hats is 5 meters.
I wound 160 turns of 1.5 mm plastic insulated copper cable.
This unit resonates around 520 kHz.

I tried with 15 watts on 522 kHz and reached about 80km with S7 during daytime.
During nighttime it was also possible, but with heavy fading as it probably skipped in the atmosphere.